22 ON CERTAIN VERMIFORM FOSSILS. 



Specimens of the two crustaceans, which make these rmis, 

 have been submitted to Mr. C. Spence Bate, and he obhgingly 

 informs me that the larger one — that which makes the broad, 

 elevated track — is a scarce animal, and was described by him 

 under the name of Bellia arenaria, in the " Annals of Natural 

 History for 1851;" but the name was afterwards changed to 

 that of Sulcator arenarius. He alludes to its habit of making 

 tracks in the sand. The smaller animal he states to be an un- 

 described species of the genus Kroyera, for which he proposes the 

 specific denomination of arenaria. Both species are figured and 

 described by that gentleman in the preceding paper. 



It has been already pointed out that the tracks, which we have 

 just seen are made by these crustaceans, are remarkably similar 

 to the vermiform impressions observed on the carboniferous 

 slabs. Indeed, the broad, raised track (PL III. fig. 1) produced by 

 Sulcator arenarius^ so closely resembles some of the fossils, that 

 it is difficult to say in what they differ. The description pre- 

 viously given of the former might, in fact, do very well for the 

 latter, only they are rarely so complicated. There are four kinds 

 of these fossil tracks. 



The first (PI. YII. c, c, c) is in the form of a simple furrow, with 

 a narrow ridge on each side ; it is small, measuring scarcely 

 more than one-eighth of an inch wide, and has a wandering, un- 

 dulating course which, however, is never very much complicated, 

 and is confined to the same horizontal plane. 



The second, which is a little wider than the above, is smooth, 

 cylindrical, and tortuous, and usually remains in relief on the 

 lower slab, but occasionally dips a little beneath the surface. 



The third (Pis. V. and VI.) is irregularly cylindrical, and though 

 sometimes much undulated, is never convoluted or very compli- 

 cated ; it is not strictly confined to the same horizontal plane, 

 but frequently sinks a little below the surface ; full-sized S2:)eci- 

 mens are half-an-inch wide, and are composed of a series of nodules 

 {a, a), which give to them an articulated appearance. The 

 nodules, which vary a little in size, are usually about half-an- 

 inch long, and are not very symmetrically or regularly formed — 



